<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<div id="app">
    <h2>{{fullName}}</h2>
</div>

<script src="../js/vue.js"></script>
<script>
    const app = new Vue({
        el: '#app',
        data: {
            firstName: 'a',
            lastName: 'b',
        },
        computed: {
            // fullName: function () {
            //     return this.firstName + ' ' + this.lastName;
            // }
            fullName: {
                set: function (newName) {
                    const tmp = newName.split(' ');
                    this.firstName = tmp[0];
                    this.lastName = tmp[1];
                },
                get: function () {
                    return this.firstName + ' ' + this.lastName;
                }
            }
        }
    })
</script>

</body>
</html>